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Gold metal
au alloy
XAU alloy
GOLD alloy
gold
Gold (Gold) is the elemental form of the chemical element gold (Au), which is a soft, golden yellow, and corrosion-resistant precious metal. Gold is one of the rarer, more precious and highly valued metals. In the world, gold is generally ounce as a unit. In ancient China, "two" as a gold unit is a very important metal. It is not only a special currency for reserve and investment, but also an important material for jewelry industry, electronics industry, modern communications, aerospace industry and other sectors.
The chemical symbol of GOLD is Au, and the financial code is XAU or gold. The name Au comes from a story about Aurora, the Roman goddess of dawn, meaning the shining dawn.
Physical property
1. Color:
gold
Gold (3 sheets)
When gold is melted, the steam emitted is greenish-yellow; Its gold powder is usually brown in the smelting process; If it is cast in thin pieces, it can transmit green light.
2. Ductility:
Unusually strong. An ounce of gold can be drawn 50 miles long, and its malleability makes it easy to cast, making it a good choice for jewelry. Gold has the strongest pull of all metals.
3. Malleability:
Second to none. It creates extremely thin gold flakes that roll up easily. An ounce of gold can be hammered as thin as 4 millionths of a foot thick and as large as 100 square feet. Ancient people hammered it into thin sheets and used it to decorate temples and palaces. All of these can explain the flexibility and malleability of gold.
The color of gold is golden, glossy metal, difficult to decompose. Density 19.3g/cm3, melting point 1064.4ºC; Good ductility, can be pressed into thin foil, has very high heat transfer and electrical conductivity, pure gold resistance is 2.4P. Pure gold has good resistance to chemical corrosion and is the best electroplating material.
As a kind of precious metal, gold has good physical properties, "true gold is not afraid of fire" is the chemical stability of gold is very high, not easy to react with other substances, do not have to worry about oxidation discoloration. Even in the molten state will not be oxidized discoloration, after cooling so golden. The density is high and the hand feels heavy. Good toughness and ductility, good conductivity. Pure gold has a gorgeous yellow color, but when mixed with other metals, the color changes greatly, such as gold copper alloy is dark red, silver alloy is light yellow or gray white. Gold is easily ground into a powder, which is why gold is dispersed in nature, and pure gold jewelry is easily worn and reduced in weight.
In the mendeleev periodic table cicc's atomic number is 79, namely gold nucleus contains 79 protons, proton positively charged. At the same time, because of the half-full rule, gold has good chemical stability, in the metal market, gold and ruthenium, rhodium, palladium, osmium, iridium, platinum and other metals collectively referred to as precious metals.
Gold is a very soft metal, but it is not as good as lead and tin. This softness makes gold very easy to work with. However, it is not ideal for decorative makers, because it is easy to scratch and tarnish the ornaments. So when gold jewelry is made, copper and silver are generally added to improve its hardness.
Gold is easily forged and malleable, and can be ground into a transparent and transparent green gold foil with a thickness of 0.001 mm. 0.5 grams of gold can be drawn into 160 meters of gold wire.
Chemical property
Gold (transition metal), gold code is XAU_USD, XAU is the chemical element code;
Crystal structure: face-centered cube structure
Atomic weight: 196.96654
,8,18,32,18,1 shell structure: 2
Electron configuration: [Xe] 4f14 5d10 6s1
Valence: + 1, + 3
Melting point: 1064.43ºC
Boiling point: 2808 ºC
Electronegativity: 2.54
Gold bar
Gold bullion
Covalent radius: 1.34A
Ionic radius: 0.85 (+ 3) A
Atomic radius: 1.79A
Atomic volume: 10.2 cc/mol
The first ionization potential: 9.2257 V
The second ionization potential: 20.521 V
Oxidation state: (3), 1
The density of 293 k: 19.32 g/cm3
Specific heat capacity: 0.128 J/gK
Heat of vaporization: 334.4 kJ/mol
Heat of melting: 12.55kJ/mol
Conductivity: 0.452X106cm·Ω
Heat conduction coefficient: 3.17W/cmK
Elastic coefficient: 78.3X103 MPa
Coefficient of thermal expansion: 14.2 X10-6 / K
Lattice parameter: 4.0786A
Mohs hardness: 2.5
Gold is chemically stable and highly resistant to corrosion. It does not react with oxygen in air even at high temperatures (except for pure oxygen under certain conditions). Gold does not react with oxygen and sulfur at high temperatures and is chemically very stable, much more stable than silver. Silver oxidizes at 1500 degrees to form silver oxide, and gold doesn't react with oxygen even above 3000 degrees. But gold is oxidized when:
1. It is located at the bottom of the river and rubbed by the sand and stone at the bottom of the river for years.
2. When the river freezes in winter, the water close to the bottom of the river is liquid, and the oxygen pressure in the water is several times higher than when it is not frozen.
3. Rivers freeze and melt year after year.
4, the oxygen at the bottom of the river is pure (4000 degrees, high pressure, catalyst), insoluble in a single hydrochloric acid, , sulfuric acid and other strong acids, only soluble in the mixed acid of hydrochloric acid and (that is, aqua regia) to generate chlorauric acid H[AuCl4].
In the presence of oxygen at room temperature, gold can be dissolved in solution containing potassium cyanide or sodium cyanide to form a stable complex M[Au(CN)2]. Gold is also soluble in solutions containing thiourea; Also soluble in acidic solution with chlorine gas. Gold does not interact with alkali solution, but can form NaAuO2 with sodium peroxide in the molten state. Gold valence is -1, -2, +1, +2, +3, +5, +7, oxide gold oxide Au2O3, chloride has gold trichloride AuCl3.
In acidic media, chlorauric acid H[AuCl4] or complex M[Au(CN)2] can be reduced to elemental gold powder by metal zinc (zinc powder or zinc wire), sodium sulfite, hydrazine hydrate, etc., alkali metal sulfide will corrode gold, producing soluble gold sulfide. Humic acid in soil and metabolites of certain bacteria can also dissolve trace amounts of gold.
Gold has a high ionization potential, it is difficult to lose the outer electrons into positive ions, also not easy to accept electrons into anions, its chemical properties are stable, and other elements weak affinity. Therefore, in nature is the existence of elemental gold state.
The average content of gold in the earth's crust is about 1.1 parts 100 million (0.0011PPm), and the content of gold in seawater is about 1 parts 100 billion (0.00001PPm). Due to the crustal movement and geological changes over several hundred million to several billion years, the gold element is rich and integrated into gold deposits. The grade of gold in the gold deposits of general industrial value is about 2-3 grams per ton. Rich ore has 5-50 g/ton, special rich mine 50-500 g/ton, and a piece of gold, a single smallest dozen grams, the largest dozens of kilograms, rare large gold hundreds of kilograms, because some shape like dog head, commonly known as dog head gold, Indian scientists have found two pieces of nearly 2.5 tons of dog head gold; Lean ore in 0.1-1 g/ton, smelting technology level of 0.5 g/ton above has industrial mining value.
Natural pure gold is rare, often containing silver, copper, iron, palladium, bismuth, platinum, nickel, tellurium, selenium, osmium and other associated elements, natural gold containing 15% silver is called silver gold, copper with 20% or more called copper gold, palladium with 5%-11% palladium gold, bismuth with 4% or more called gold.
Gold is sulfurophilic and often closely associated with sulfides such as pyrite, arsenopyrite, galena, stibnite, etc. It is easy to form metal intercompounds with sulfurophilic silver, copper and other elements.
The following is the chemical equation for gold
Gold can be oxidized by purer chlorine and fluorine (only by heating)
2Au+3Cl2= heating =2AuCl3
2Au+3F2=2AuF3
Gold will not be eroded and discolored by sulfur and oxygen at high temperature alone, but it will be oxidized under certain conditions, or react very slowly with oxygen at high temperature of 4000 degrees, under pressure and with catalyst: It can be regarded as no reaction, because in general, few flames can exceed 3500 degrees, and gold melts above 1000 degrees, so it is generally believed that real gold is not afraid of fire, that is, gold does not react with oxygen at high temperature, gold and sulfur, bromine, iodine, nitrogen reaction temperature is higher, and chlorine gas, fluorine gas, royal water reaction temperature is lower.
4Au+3O2= high temperature and high pressure, catalyst =2Au2O3
rust
Although gold itself is not corroded, but its chemical affinity with sulfide is very strong, easy to absorb hydrogen sulfide acid gas in the air, the surface of the dark color such as orange, brown red and other colors are possible. The production of gold products needs to go through many complicated processes.
Take gold bars and gold coins for example. They all have to go through melting, pressing, cutting, holding, fading, frying, polishing, pressing, holding and other processes. The working environment of these processes cannot be vacuum environment. Each link may encounter dust in the air and impurities adhering to the blank of the product. These impurities may become erythematous after a period of storage without faded fire and pickling.
In daily appreciation, do not directly touch the gold products with your hands. Once there is erythema, you can ask professionals to burn the gold products on the fire, you can solve the problem, and basically will not affect the quality of gold products.
In addition to red spots and dark spots, gold products can sometimes have white spots, especially gold jewelry.
This is mainly because consumers tend to put gold jewelry randomly in the drawer, in case there are substances, will immediately form a large area of white spots, especially women in the use of containing cosmetics, long-term contact will also produce white spot gold products, if worn with platinum and silver jewelry at the same time after a long time of friction on their surface will also produce white spots.
Four-germplasm field
Pure gold
Pure gold
Cooked gold is gold after smelting and purification, generally high purity, fine density, some can be directly used in industrial production.
Common are gold bars, gold bars, gold ingots and a variety of different ornaments, utensils, gold coins and industrial gold wire, gold flakes, gold plates and so on.
Due to different uses, the required color is different, or because there is no purification equipment, and only melt unpurified, or the purity is not enough, the formation of gold with different color. It is customary to divide ripe gold into pure gold, pure gold and colored gold according to its fineness.
After purification to achieve a very high purity of gold called pure gold, gold generally refers to more than 99.6% of the pure gold.
First, the meaning of pure gold and pure gold is similar, but because of the difference in time and place, the standard of pure gold is different. The gold sold in the international market, the completion of 99.6% is called pure gold. And the territory of the red gold in general between 99.2%-99.6%.
Second, color gold, also known as "secondary gold" and "tide gold", refers to the lower color of gold. Depending on the content of other metals, the gold can be 99% as high as 30% as low.
According to the different division of other metals, ripe gold can be divided into clear gold, mixed gold, k gold and so on. Clear gold refers to gold only mixed with silver, regardless of the level of color collectively known as clear gold. Clear gold is more common in gold bars, gold ingots, gold bars and all kinds of utensils and gold ornaments.
3. Mixed gold refers to gold containing copper, zinc, lead, iron and other metals in addition to silver. According to the different types and amounts of metal contained, it can be divided into small gold, large gold, bronze gold, lead gold, etc.
Four, k gold refers to silver, copper according to a certain proportion, in accordance with the formula of full gold 24k gold prepared into gold. Generally speaking, the more k gold silver proportion, the more green color; Copper proportion is large, the color is purple.
The percentage expressed by the value of K is only a rough number, and is not required to be very accurate. And most of the custom is to use even K value, such as 24K, 22K, 20K, 18K and so on. 18K means that 18 of the 24 alloys contain gold, equivalent to about 75% of the content. Calculation method of K gold: The formula of K gold reduced gold content is: K value ÷24×100% (i.e. K value ×4.1667%)
fineness
The purity of gold and its products is called "fineness" or "fineness".
In 200 BC, the Greek mathematician Archimdes had trouble determining whether a crown was made of pure gold. While bathing in a bathtub, he discovered what later became known as Archimedes's law of specific gravity: objects immersed in liquid experience upward buoyancy; The amount of buoyancy is equal to the weight of the liquid it displaces. This successfully confirmed whether the king's custom-made crown was made of pure gold. So, how to express the purity of gold.
1 Use "carat gold" to indicate the purity of gold
The national standard GB11887-89 stipulates that the gold content per carat (abbreviation of English carat, German karat, often written as "k") is about 4.166%, so the gold content of each carat is (national standard in brackets) :
8k=8*4.166%=33.328% (333‰)
9k=9*4.166%=37.494% (375‰)
10k=10*4.166%=41.660% (417‰)
12k=12*4.166%=49.992% (500‰)
14k=14*4.166%=58.324% (583‰)
18k=18*4.166%=74.998% (750‰)
20k=20*4.166%=83.320% (833‰)
21k=21*4.166%=87.486% (875‰)
22k=22*4.166%=91.652% (916‰)
24k=24*4.166%=99.984% (999‰)
24-karat gold is often considered pure gold, becoming "1000‰", but the actual gold content is 99.99%, discounted to 23.988k.
2. Write about the purity of gold
Some of the gold jewelry has written marks, which are as follows:
Full gold -- the gold content is not less than 990‰
Gold - the gold content is not less than 999‰
Some directly hit the actual gold content.
3. Use fractions to indicate the purity of gold
If marked as 18/24, the resulting color is 18k (750‰).
If marked as 22/24, the resulting color is 22k (916‰).
4. Use Arabic numerals to indicate the purity of gold
Such as 99 -- means "enough gold"
Such as 999 - means "a thousand gold"
China has regulations on gold products and identification plates, the general requirements of the production enterprise code, material name, content imprint, no imprint for unqualified products. The same is true internationally. But for some very small products are also allowed not to mark.
Cleaning method
1. Apply a thin layer of nail polish to protect the luster of gold ornaments.
2, if the surface has a black silver film, available salt 2 grams, baking soda 7 grams, bleach powder 8 grams, water 60 ml, prepared into the "gold cleaning agent", put the gold jewelry in a bowl, into the cleaning agent, 2 hours later, the gold jewelry out, with water (preferably not hard water) after rinsing, buried in wood chips dry, and then wipe with a soft cloth.
3. Gem-encrusted ring Roll a piece of cotton with a Popsicle or matchstick, wet it in the mixture of toilet water and glycerin, scrub the gemstone and its frame, and then polish the ring with a flannel. Do not use a sharp blade to scrape.
4. Mix salt and vinegar to make a cleaning agent and use it to
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